1. Field of the Invention
The present invention relates to a color image forming apparatus and process using an intermediate image transfer in an electrophotographic process, typically utilized by copying machines, printers, facsimiles, etc. Specifically, the present invention relates to a color image forming apparatus and process which enables the formation of color images for a plurality of recording mediums on the intermediate transfer drum.
2. Description of the Related Art
Japanese Patent Publication No. 2-28867 discloses a color image forming apparatus which has a photoreceptor drum for forming images for two recording mediums. In accordance with the disclosure of this publication, during the image formation process of the high speed printing, the second image is formed on the photoreceptor immediately succeeding the formation of the first image on the same photoreceptor. The length of the photoreceptor""s circumference is sufficient for forming consecutive images for two recording mediums.
When the color image forming apparatus constructed according to Japanese Patent Publication No.2-28867 is used for replicating the same image, a relatively high forming speed is realized for forming this image on the photoreceptor. However, when different images have to be replicated, the throughput decreases, because formation of each succeeding image does not start until the image processing of its preceding image is finished.
To solve the above problem, the applicant of the present invention has proposed a color image forming apparatus shown in Japanese Unexamined Patent Publication No. 2000-47452. The apparatus disclosed in Japanese Unexamined Patent Publication No. 2000-47452 has an intermediate transfer drum having a circumference sufficient to form images for two recording mediums on the intermediate transfer drum, where the throughput is increased by suppressing the second image formation in response to the first image processing time.
However, the image forming apparatus according to Japanese Unexamined Patent Publication No. 2000-47452 has not taken into consideration the case of mixed monochromatic-and-color printing. When a mixed monochrome and color printing is performed on the apparatus constructed in accordance with this patent publication, for example, when the apparatus processes a preceding image containing full four colors following by a succeeding monochromatic image, a problem may occur where the image output of the succeeding monochromatic image may outrun the output of the preceding image causing out-of-order pages.
Another problem is that the throughput of the color image forming apparatus according to Japanese Patent Publication No. 2-28867 is higher than the throughput of the color image forming apparatus according to Japanese Unexamined Patent Publication No. 2000-47452 when the same images are replicated.
A further problem of the apparatus disclosed in Japanese Unexamined Patent Publication No. 2000-47452 is that, the adjustment of processing timing with timing of after-processing devices, for example, doublesided printing device, sorter, stacker, etc., is complicated when the first and second images are formed on the photoreceptor, and the timing of the second image formation is delayed during the image processing.
Still another problem with the apparatus of Publication No.: 2000-47452 is that the picture quality may be reduced because of the complicated control of development, transfer, fixing, cleaning, etc. accompanying the image formation, and because the load of the photoreceptor and intermediate transfer drum increasingly varies.
A yet further problem arises when a scanner is installed as an external unit and the apparatus is used as a copying machine. An output delay may then occur if the user tries to copy the images by repeatedly pushing the xe2x80x9cprintxe2x80x9d button.
The present invention is made in light of the problems mentioned above. It is an object of the present invention to enable high quality color image processing at high throughput while replicating the same image or printing different images.
It is another object of the present invention to provide color image processing in which timing synchronization is easy to perform during the image processing even when an external option, for example a scanner, is installed.
It is a further object of the present invention to provide a color copying apparatus which does not cause output delays when a scanner is installed as an external unit and the apparatus is used as a copying machine.
It is still a further object of the present invention to provide a color image forming apparatus which can perform printing while preserving the right printing order of pages without reduction of throughput even in the case of mixed monochrome-and-full-color printing.
It is still a further object of the present invention to provide a high throughput color image forming apparatus which can perform printing of images for a plurality of recording mediums and where the images are formed on the intermediate transfer drum.
To accomplish the above enumerated objects, an image forming apparatus is provided in accordance with the present invention, which can form images for a plurality of recording mediums. A color image forming apparatus for printing color images for a plurality of recording mediums having one or more photoreceptors for forming toner images of different color toners. The toner images are superimposed onto the intermediate transfer drum having a length of circumference such that a plurality of color images for the plurality of recording mediums can be held on this intermediate transfer drum. The superimposition of colors is done by consecutively repeating the primary transfer of each toner developed on the photoreceptor to the intermediate transfer drum. The toner images are formed on the photoreceptor and transferred to the intermediate transfer drum consecutively if the color images to be printed are solely of a specific monochrome color. If however, color images of a polychrome color or a monochrome color other that the specific monochrome color are to be printed, the toner images are formed and superimposed onto the intermediate transfer drum with a timing delay equal to a predetermined number of rotations of the intermediate transfer drum.
With the provided configuration, a color image forming apparatus controls printing and eliminates the problem of the later page outrunning the preceding page even in the case of mixed monochrome and full-color printing. The provided apparatus can further perform an accurate printing at high throughput.
Further, the provided color image forming apparatus allows the superimposed color images for a plurality of recording mediums to be formed within the same image forming cycle on the intermediate transfer drum.
The mentioned specific monochrome may be selected to be any of the monochromes provided in the apparatus, for example black or magenta.
The provided color image forming apparatus has plural image formation control means for determining whether the formation of the images is possible on the intermediate transfer drum. A first of two consecutive color images for a plurality of recording mediums is formed on the intermediate transfer drum if the plural image formation control means determine that this formation is possible. A succeeding superimposed color image may be formed on the intermediate transfer drum after the first superimposed color image if the plural image formation control means determine that the formation of these superimposed color images is not possible.
A method of forming color images is also provided in accordance with the present invention. The color images are formed in the provided color image forming apparatus. The apparatus preferably allows its user to select a consecutive formation of images for a plurality of recording mediums on the intermediate transfer drum or alternatively to select a delayed formation of these images on the intermediate transfer drum. When the delayed formation is selected, there is a time delay between formation of two consecutive images. Switching between different types of image formation is preferably done according to the operational mode of the provided apparatus. The time delay between the formation of the two consecutive images may be set beforehand and preferably is equal to a predetermined number of rotations of the intermediate transfer drum. Images for three or more recording mediums may be held on the provided intermediate transfer drum.
Further features and advantages of the invention will become evident to one skilled in the art upon reading of the detailed description of the invention, which is given below by way of example only and with reference to the accompanying drawings.